Short answer: Taken PWO, creatine can help you gain mass by putting more water into your muscles. This helps your leverages, increases your LBM, gives your muscles a more 'full' look without actually increasing your strength levels or the size of your muscle fibers (myofibullar hypertrophy, I believe. Horrible spelling though).
Long answer: your muscles are made of part shit (solute) part water (solvent). Generally, it likes to keep things pretty much at homeostasis (the same levels). When you take creatine, and it gets into the cells, it increases the levels of shit (solute) in your muscles. Your body doesn't like being out of homeostasis, so to adapt, it draws in water (solvent) to balance out the ratios. This doesn't really do anything besides add weight, and maybe increase your leverages. It isn't hypertrophy, sarcoplasmic or myofibullar, it's just water. So it's called 'water weight'.
Honestly, don't worry about it. Your weight will go up without significantly impacting your BF levels. When you cut, you'll lose the water weight. When you start doing carbs again, you'll gain it back. It's basically one of things you learn to factor out, even though it's pretty cool to gain ten pounds after a carb-load due to glycogen replenishment and water-weight.